Ideals, central tendency, and frequency of instantiation as determinants of graded structure in categories.

Three possible determinants of graded structure were observed on common taxonomic categories and goal- derived categories (1) an exemplar is similarity to ideals associated with goals its category serves (2) an exemplars's similarity to the central tendency of its category, and (3) an exemplar's frequency of instantiation. It is proposed that graded structures do not reflect invariant structures associated with categories but instead reflect people's dynamic ability to construct concepts.